Paleontological Research in Tanzania

Introduction

The Permian and Triassic periods (approximately 299 Mya to 199 Mya) are critical times in Earth history. Among the important events that occur during this interval are a major diversification of ancient mammal relatives called non-mammalian synapsids, a transition between from an ice-house global climate regime to a greenhouse climate regime, the largest mass extinction in Earth history, the origin of mammals, and the origin and early diversification of dinosaurs. In 2007 and 2008 Field Museum researchers Ken Angielczyk and Bill Simpson were part of an international team of scientists that traveled to the Ruhuhu Basin in southern Tanzania to collect fossils and geological data from Upper Permian and Lower Triassic rocks to gain new insight into the causes of and recovery from the end-Permian mass extinction in terrestrial vertebrate-dominated communities.

The Ruhuhu Basin

The Ruhuhu Basin is an ancient rift basin in which Permian and Triassic sedimentary rocks were deposited. Of particular interest to our team are the rocks of the Permian-age Ruhuhu Formation and Usili Formation, and the Triassic-age Manda beds because these rocks preserve fossils of terrestrial vertebrates.

Lithostratigraphy of the Ruhuhu Basin. Formations of interest are highlighted. Modified from Wopfner (2002). Courtesy of C. Sidor.

Fossils were first discovered in the Ruhuhu Basin by Gordon. Stockley in the 1930's. Subsequent collections of fossils were made in the mid-1930's by Rex Parrington of Cambridge University and Ernst and Maria Nowack, who were jointly sponsored by Cambridge University and the University of Tübingen. These collections showed that the Permian and Triassic faunas of the Ruhuhu Basin included many synapsids, as well as rarer reptiles and amphibians, and were similar to those known from the Karoo Basin of South Africa. In 1963, an expedition sponsored by University College London and the British Museum of Natural History (now The Natural History Museum) collected additional fossils from the basin, including new synapsids and archosaurs (the group that includes dinosaurs, birds, and their relatives). After 1963, no large collections of vertebrate fossils were made from the Ruhuhu Basin until our team began our research in 2007.

Fossils of the Ruhuhu Formation

Although there are older reports of plant fossils from the Ruhuhu Formation, the first report of vertebrate fossils was made by members of the 1963 expedition (Attridge et al., 1964; Cox, 1964; 1991; Cruickshank, 1986; Gay and Cruiskshank, 1999).

These specimens have not yet been formally described, and our team questioned whether they originated in the Ruhuhu Formation, or the overlying Usili Formation (Sidor et al., 2010). In 2008, our team discovered fragmentary fossils of dinocephalian synapsids, anomodont synapsids, and temnospondyl amphibians in the Ruhuhu Formation. The dinocephalian specimens are especially important because they are the first members of this group to be found in Tanzania, and they suggest a Middle Permian age for the Ruhuhu Formation (Simon et al., 2010). The anomodont and amphibian material is still currently under study.

Fossils of the Usili Formation

Skull of the anomodont synapsid "Dicynodon" huenei found in the Usili Formation. Photo by K. Angielczyk

The great majority of Permian tetrapod fossils collected by previous workers were found in the Usili Formation. The fauna is dominated by synapsids, especially anomodonts and gorgonopsians, although therocephalians and cynodonts are rarer components of the fauna. Pareiasaurs (herbivorous armored reptiles) also are present, as well as a distinctive armored amphibian called Peltobatrachus.

Our team collected a large number of anomodont fossils in the Usili formation, including at least one new species. We also discovered the first burnetiamorph (a type of carnivorous synapsid characterized by bony lumps on the skull) from Tanzania (Sidor et al., 2010), new specimens of the cynodont Procynosuchus (Weide et al., 2009), pareiasaurs, large saber-toothed gorgonopsians, and fragmentary specimens of Peltobatrachus.

Sterling Nesbitt shows off a canine tooth from a large gorgonopsian synapsid that he just found in the Usili Formation. Photo by R. Smith.

The Usili Formation tetrapod fauna is similar to coeval faunas in the Karoo Basin of South Africa in being dominated by synapsids, but also differs in having several endemic species and a mixture of broadly-distributed species that do not co-occur in South Africa.

Skull of the cynodont synapsid Scalenodon angustifrons found in the Lifua Member.Photo by K. Angielczyk.

The Manda beds are of Middle Triassic age (approximately 240 Mya),and consist of two named members, the Kingori Sandstone and the Lifua Member. Very few fossils have been collected from the Kingori Sandstone, and our team has spent little time working in this unit. The Lifua Member is much richer, with previous workers recovering a mixture of anomodont and cynodont synapsids, as well as several archosaurs and rhynchosaurs (a group of herbivorous reptiles related to archosaurs). Our team collected a few fragments of a very large amphibian, some rhynchosaur specimens, and some anomodont material, mostly representing an animal called Sangusaurus. Cynodont specimens also are common at certain localities, and we have representatives of at least six species. Most importantly, we discovered several archosaurs, including relatives of dinosaurs and crocodiles. To date, we have described one of these archosaurs, the dinosaur relative Asilisaurus kongwe (Nesbitt et al., 2010).

Artist's reconstruction of Asilisaurus kongwe (foreground). The sail-backed archosaur in the background is Hypselorhachis mirabilis. Image by M. Donnelly.

Asilisaurus is a small, lightly built herbivore, but it is one of the closest relatives of dinosaurs known. Furthermore, its presence in the Middle Triassic implies that dinosaurs must have originated by this time, which is about ten million years earlier than previously thought. The other archosaurs are under study, and when combined with previously described material, they suggest that the Middle Triassic fauna of Tanzania had a much greater diversity of archosaurs than contemporary faunas in South Africa.

The End-Permian Mass Extinction

Approximately 252 Mya, at the end of the Permian Period , terrestrial and marine ecosystems were struck by the largest mass extinction in Earth history. Although the exact cause of the extinction is still debated, it appears likely that massive volcanic eruptions in Siberia were the ultimate cause, with global warming and changes in ocean chemistry as important kill mechanisms for marine and terrestrial animals and plants. Our picture of how terrestrial vertebrate faunas were affected by this event and how they recovered primarily comes from the Karoo Basin of South Africa and the fore-Ural region of Russia. A major goal of our work in Tanzania is to document the Permo-Triassic transition in the Ruhuhu Basin for comparison with the better-studied South African and Russian records.

Although there appears to be a hiatus in the early Triassic fossil record in the Ruhuhu Basin, we can make inferences about the effects of the extinction by comparing the Late Permian Usili Formation fauna to that known from the Lifua member. The Usili Formation fauna is quite comparable to that seen in South Africa, with synapsids dominating in both diversity and abundance. In addition, the synapsids in both places appear to have been strongly affected by the extinction, because many groups become completely extinct, and even the survivors show patterns of turnover (i.e., replacement of older species by new species). Despite this apparent similarity in the effects of the extinction, the recovery process in South African and Tanzania appears to have proceeded differently. South African faunas in the Early and Middle Triassic consist of a fairly balanced mix of synapsids, reptiles, and amphibians, with only a few species of archosaurs present. In contrast, a much greater diversity of archosaurs is present in Tanzania in the Middle Triassic, and these species show greater signs of ecological differentiation than their South African contemporaries (which were all carnivores). Synapsids are relatively common in Tanzania as well, but amphibians and small reptiles are rare to completely absent. We are now investigating why the recovery process proceeded in different ways in Tanzania and South Africa, and are also studying Permian and Triassic communities in Zambia to see whether they more closely resemble the patterns observed in Tanzania or South Africa.

I Dig Tanzania!

Students in New York City conduct their virtual fossil dig in Teen Second Life. Photo courtesy of Global Kids.

During the 2008 field season, our team collaborated with The Field Museum's Education Department, the Biodiversity Synthesis Center, and Global Kids on a digital learning pilot program called “I Dig Tanzania!” Through this program, groups of high school students followed the progress of our fieldwork in real time by watching short videos we filmed and uploaded by satellite internet connection, and by talking to us on satellite phone calls. The students also used the 3D virtual world Teen Second Life to participate in a virtual fossil dig of their own, which had activities designed to replicate various aspects of our research, and to build virtual museums exhibits detailing the results of their work. In addition to learning about science, the students studied Tanzanian history, politics, and culture, and received behind-the-scenes tours at museums. I Dig Tanzania! was made possible by funding from The John D. and Catherine T. MacArthur Foundation.

Acknowledgments

Our fieldwork in 2007 was funded by National Geographic (CRE #7587-05 to C. A. Sidor), the National Science Foundation (NSF Graduate Fellowship to S. J. Nesbitt; NSF DBI-0306158 to K. D. Angielczyk), and the Evolving Earth Foundation (Evolving Earth Foundation grant to S. Nesbitt). Our fieldwork in 2008 was funded by The Grainger Foundation (grant to K. D. Angielczyk), and I Dig Tanzania! was funded by The John D. and Catherine T. MacArthur Foundation. Our research in Tanzania is made possible by the support of the Tanzanian Commission for Science and Technology, the Tanzanian Ministry of Natural Resources and Tourism, and Dr. Charles Sanaane (University of Dar es Salaam).